1. Field of the Invention
The present invention relates to a shuttle apparatus which reciprocates to effect printing in a line printer or other similar printer.
2. Description of the Related Art
In line printers or other similar printers, a print shuttle unit equipped with a print head needs to reciprocate at high speed, and a linear motor is used as a device for driving the print shuttle unit.
Therefore, a row of electromagnetic coils are attached to a print shuttle unit movable along a stay shaft with a print head mounted thereon, and a row of permanent magnets are secured to a base frame so as to face the electromagnetic coils, thereby forming a linear motor.
In operation, as current is passed through the electromagnetic coils attached to the print shuttle unit, thrust is induced in the electromagnetic coils according to the Fieming's left-hand rule. By properly controlling the current supplied to the electromagnetic coils, the direction of the thrust is changed, thus causing the print shuttle unit to reciprocate.
However, since the electromagnetic coils are mounted on the print shuttle unit, if the volumetric capacity of the electromagnetic coils is increased in order to raise the output of the linear motor, the print shuttle unit becomes correspondingly heavier, resulting in an increase in the load. Accordingly, the speed of the reciprocating motion cannot be raised so high as expected.
Further, an assembly of lead wires for connecting the electromagnetic coils to a power supply is secured at one end thereof to the base frame, while the other end of the lead wire assembly reciprocates together with the print shuttle unit. It is therefore likely that the lead wires will be damaged and disconnected by the repeated reciprocating motion.
In addition, since the print shuttle unit is considerably heavy in weight, the high-speed reciprocating motion thereof causes vibration of the whole printer.
To cope with this problem, a balance shuttle unit is generally employed. More specifically, a balance shuttle unit, which is formed with approximately the same weight as that of the print shuttle unit, is driven in linked relation to the reciprocating motion of the print shuttle unit so that these two shuttle units move parallel to each other in opposite directions, thereby canceling reaction force generated in the base frame of the printer by the reciprocating motion of the print shuttle unit. Thus, generation of vibration is suppressed.
However, if the print shuttle unit and the balance shuttle unit move parallel to each other in opposite directions, rotation moment is induced by the motions of the two shuttle units. As a result, rotation vibration is generated in the whole printer, causing the print quality to be degraded, for example, by undesired movement of printing paper.